If you are the principal applicant, you just land as a PR and it is completely irrelevant to your PR if your family lands or not. If they choose to let their PR visas expire, that is fine and they will not become PR. If they choose to make the trip to land and then go back home, that is fine too. They can spend up to 3 years outside as PR's before they must return to Canada in order to meet the RO (residency obligation) in order to keep their PR. If they don't want to keep it, they simply don't return.
If some other family member is the principal applicant and you are a dependent on their application, the principal applicant must land in order for you to land and after that, it does not matter what they do.